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  • Tool blackening.

    I stuck a post into a different thread about a tool blackening method I was not familiar with. I found it on another site, and tried it, with good results. It probably deserves its own post, so here it is.

    "Oil blackening".

    Basically, heat the steel up until it is through the straw, brown, blue, and purple oxide stages, and has turned to a steely gray color. Then drop into oil. Old stinky gear oil, used motor oil, etc is fine and maybe better.

    The parts, if heated correctly, will come out a nice black, sometimes with bluish or purple highlights.

    The results:



    The "before" picture (including some other tooling):

    CNC machines only go through the motions

  • #2
    Nice looking finish on those parts.

    I first heard about oil blackening many years ago from a blacksmith who did mostly ornamental work. And yes, as I recall, it was the old used motor oil that gave the best results.

    Comment


    • #3
      For more deterministic results, you can bypass the toxic mess of old motor oil and just add sulphur to nice clean oil. I have a very old book around here somewhere that details exactly how.

      Or.. Use old school "dark cutting oil". Contains a lot of sulphur.
      Last edited by lakeside53; 04-23-2017, 01:19 AM.

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      • #4
        Sul -Flo..
        I find the hot dip in oil seems to help against rust a bit..
        I like the old splotchy treatment on some Starrett stuff..might by cyanide..

        Comment


        • #5
          Originally posted by lakeside53 View Post
          ....toxic mess of old motor oil ......
          LOL

          The stuff I used was likely mostly 90wt gear oil, with sulfur EP additives. It came from the bottle labelled as " "oil" ", which is where whatever is drained out of old small engines and so forth goes. Last thing drained was a gearcase, IIRC

          Toxic..... maybe..... Gear oil isn't exactly distilled water either. Nor is dark cutting oil, etc. And hot parts can cause burns, hot oil may splatter and cause burns, or catch fire (maybe). Your results may differ, don't try this at home, folks...... etc.

          I didn't try it at home, I was out in the driveway.

          "just add sulfur"... How did you propose to do that? And who said sulfur was gonna be in used motor oil but not in new?

          Anyhow, it is amazing how a black finish makes tooling that you cob up in the shop look professional. I like it.

          I don't quite understand what the oil has in the process, it does not appear to be contributing carbon as a layer on top of the steel or anything like that. But the steel goes in grey and hot, comes out warm and black.

          Some seem to say the oil temp makes a difference. Of those, some say oil that is too hot does not give a good black finish, others say cold oil gives a bad finish. Could be both are right, but I do not know what the real story is, and I am not clear on what gives the black color. Could be just the gray finish with oil soaked into it.
          Last edited by J Tiers; 04-23-2017, 01:53 AM.
          CNC machines only go through the motions

          Comment


          • #6
            I've been doing this method for years.
            The best is used diesel oil. Believe me, i've tried 'em all.
            The worst for "blackening" is new motor oil. Comes out as a brown transparent colour.
            Leave the hot part in the oil until it is cool enough to touch manually. Longer the better.

            Comment


            • #7
              [QUOTE=J Tiers;1112777]Last edited by J Tiers; Today at 10:53 PM.
              Solly JR
              Last edited by JRouche; 04-24-2017, 07:39 PM.

              Comment


              • #8
                Black oxide*or*blackening*is a*conversion coating*for ferrous materials, stainless steel,*copper*and copper based alloys,*zinc,*powdered metals, and*silver solder.[1]*It is used to add mild corrosion resistance, for appearance and to minimize light reflection.[2]*To achieve maximal corrosion resistance the black oxide must be impregnated with oil or wax.[3]*One of its advantages over other coatings is its minimal buildup.-From Wikipedia. I used the old oil method when I first started to harden 🔪 knife blades. Another trick you might try is an electrolysis bath if you have not already done so. That leaves a nice finish and could be further protected with oil or wax and. I think the main benefit for me is the ability to walk away while it's does all the work.

                Sent from my RCT6513W87 using Tapatalk

                Comment


                • #9
                  I hardened some small 4140 parts once with new motor oil, non detergent type I think. The parts came out a beautiful dark black and very uniform. The project then sat for a long time and unused bits of the same 4140 rusted in my shop while the hardened parts remain pristine.

                  Comment


                  • #10
                    I've tried oil blackening before, usually when I quench a part after heating it to cherry red. The results are usually a black finish but it seems to flake off in spots and has little to no durability. If I want to blacken something and do a nice job I do it in my little hot blue tank set up.

                    JL..................

                    Comment


                    • #11
                      There is a formula if memory serves me that uses a solution of selenium dioxide. It's a cold solution and made for blacking steel and re-bluing guns with warn spots
                      https://www.birchwoodtechnologies.co...Fc-1wAodRPUIjw
                      http://www.mmsonline.com/articles/do...old-blackening
                      http://www.caswellplating.com/metal-...xide-kits.html

                      As an alternative for those that may not have the heat requirements of a torch or want the mess of oil.
                      Tom

                      Comment


                      • #12
                        Originally posted by tincture500 View Post
                        There is a formula if memory serves me that uses a solution of selenium dioxide. It's a cold solution and made for blacking steel and re-bluing guns with warn spots
                        https://www.birchwoodtechnologies.co...Fc-1wAodRPUIjw
                        http://www.mmsonline.com/articles/do...old-blackening
                        http://www.caswellplating.com/metal-...xide-kits.html

                        As an alternative for those that may not have the heat requirements of a torch or want the mess of oil.
                        Tom
                        Parkerizing is also worth to mention. A lot less hazarous chemicals than caustic hot bluing and cheaper raw materials.
                        Location: Helsinki, Finland, Europe

                        Comment


                        • #13
                          Originally posted by J Tiers View Post


                          "just add sulfur"... How did you propose to do that? And who said sulfur was gonna be in used motor oil but not in new?

                          .
                          You can buy powdered sulphur easily- even a garden store will likely have it for controlling black spot on roses.

                          It's the sulphur additives or accumulations that make "good black". I sure there's other junk that has variable results, but my point was you can make it deterministic. Diesel sump works (toxic) because of the sulphur from the fuel (less now than the old days). Using clean oil and adding sulphur is a very old process that works well. I did some 30 years ago with predictable results, but another guy had prepared the oil. I don't have the book in front of me, but you basically melt powdered sulphur in hot oil. It melts not much hotter than boiling water. I'll find it and scan.
                          Last edited by lakeside53; 04-23-2017, 11:19 AM.

                          Comment


                          • #14
                            Originally posted by JRouche View Post
                            QUOTE=J Tiers;1112777]Last edited by J Tiers; Today at 10:53 PM.

                            No need to be an ass Jerry. Folks are giving good advice. Listen up. JR
                            ?????????????????????????????
                            Last edited by J Tiers; 04-23-2017, 01:22 PM.
                            CNC machines only go through the motions

                            Comment


                            • #15
                              Originally posted by zachary.s.hodge View Post
                              Black oxide*or*blackening*is a*conversion coating*for ferrous materials, stainless steel,*copper*and copper based alloys,*zinc,*powdered metals, and*silver solder.[1]*It is used to add mild corrosion resistance, for appearance and to minimize light reflection.[2]*To achieve maximal corrosion resistance the black oxide must be impregnated with oil or wax.[3]*One of its advantages over other coatings is its minimal buildup.-From Wikipedia. I used the old oil method when I first started to harden 🔪 knife blades. Another trick you might try is an electrolysis bath if you have not already done so. That leaves a nice finish and could be further protected with oil or wax and. I think the main benefit for me is the ability to walk away while it's does all the work.

                              Sent from my RCT6513W87 using Tapatalk
                              Yes, blackening works just like that, it is known as a conversion coating. However, it is something completely different than dipping a hot part in oil.
                              Amount of experience is in direct proportion to the value of broken equipment.

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